The EVO 70 is certainly a magic board. All versions that both people in the 80+ range and in the sub 70 range praise its versatility says a lot.
Your right in that the 70 did not change a lot the first years. The the squash tail 04 feel rather similar to the 05 which in turn in identical to the 06. The 07 is pretty similar in feel to, but definitely a bigger change compared to the 04-05. Especially it is noticeably smoother in the top turn and the shape is sleeker and more harmonic, I would say. For 08 the shape is different once again, the extra v from 07 is still there, but the board is a tad thicker overall and with a slight tweak to the outline. This makes the board feel a bit bigger in size, but I still think its smoother off the top than the 06.
But again, the general feel of the board is still the same and although the last two years have offered bigger changes, I have still felt perfectly at home on the new boards each time.